Semiconductor device and method for manufacturing the same

ABSTRACT

A semiconductor device comprises a conductor film and a capacitor comprising a lower electrode provided on the conductor film. The conductor film includes a first conductive film containing a first metal, a second conductive film containing a second metal on the first conductive film, and an oxide film of the second metal on the second conductive film. The oxide film of the second metal has a lower electric resistivity than an oxide film of the first metal.

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2011-267690 filed on Dec. 7, 2011, thedisclosure of which are incorporated herein in its entirety byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device and a method formanufacturing the semiconductor device.

2. Description of the Related Art

DRAM (Dynamic Random Access Memories) has been used as semiconductorstorage devices. The DRAM includes a plurality of memory cells each ofwhich is formed of a transistor and a capacitor. The capacitor includesa capacitive insulating film between a lower electrode and an upperelectrode. Charge is held in the capacitive insulating film to storeinformation.

FIG. 7 and FIG. 8 in JP2011-204751A disclose forming an aluminum oxidefilm and a zirconium oxide film by an ALD method respectively. The ALDmethod forms one molecular layer of an aluminum oxide film or azirconium oxide film by carrying out a cycle including supplyingmaterial gas, purging the material gas, supplying O₃ gas, and purgingthe O₃ gas. Then, the cycle is repeated a plurality of times to form analuminum oxide film and a zirconium oxide film with respective desiredfilm thicknesses.

JP2000-31404A discloses that a metal oxide film such as an IrO₂ film, anITO film, an RHO₂ film, an RuO₂ film, or an MoO₃ film is used as a partof the lower electrode (Paragraph [0013]).

In the DRAM, the connection between the lower electrode of the capacitorand a capacitive contact plug positioned under the lower electrode isestablished via a pad in order to ensure a pitch aligning margin(hereinafter occasionally referred to as a “contact pad”). The pad needsto have reduced resistance, and thus a metal layer, particularlytungsten, is used as a common pad material. Furthermore, as a method forforming the lower electrode, there is used the ALD method, which isexcellent in step coverage and which can deal with miniaturization. Whena metal oxide film is formed as the lower electrode by the ALD method,as described in JP2000-31404A, O₃ gas, which has high oxidizability, isused to oxidize a metal material. However, the O₃ gas oxidizes the padformed of tungsten or the like to increase the electric resistivitythereof, thereby inhibiting the electric continuity between the lowerelectrode and the pad.

SUMMARY

In one embodiment, there is provided a semiconductor device comprising:

-   -   a conductor which includes a first conductive film containing a        first metal, a second conductive film containing a second metal        on the first conductive film, and an oxide film of the second        metal on the second conductive film; and    -   a capacitor comprising a lower electrode provided on the        conductor,    -   wherein the oxide film of the second metal has a lower electric        resistivity than an oxide film of the first metal.

In another embodiment, there is provided a semiconductor devicecomprising:

-   -   a first conductive film containing a first metal;    -   a second conductive film containing a second metal on the first        conductive film;    -   an oxide film of the second metal on the second conductive film;        and    -   a third conductive film on the oxide film of the second metal,    -   wherein the oxide film of the second metal has a lower electric        resistivity than an oxide film of the first metal.

BRIEF DESCRIPTION OF THE DRAWINGS

The above features and advantages of the present invention will be moreapparent from the following description of certain preferred embodimentstaken in conjunction with the accompanying drawings, in which:

FIG. 1 illustrates a semiconductor device according to a first exemplaryembodiment;

FIG. 2 illustrates the semiconductor device according to the firstexemplary embodiment;

FIG. 3 illustrates a step of a method for manufacturing a semiconductordevice according to the first exemplary embodiment;

FIG. 4 illustrates a step of the method for manufacturing asemiconductor device according to the first exemplary embodiment;

FIG. 5 illustrates a step of the method for manufacturing asemiconductor device according to the first exemplary embodiment;

FIG. 6 illustrates a step of the method for manufacturing asemiconductor device according to the first exemplary embodiment;

FIG. 7 illustrates a step of the method for manufacturing asemiconductor device according to the first exemplary embodiment;

FIG. 8 illustrates a step of the method for manufacturing asemiconductor device according to the first exemplary embodiment;

FIG. 9 illustrates a step of the method for manufacturing asemiconductor device according to the first exemplary embodiment;

FIG. 10 illustrates the state of a pad during formation of a lowerelectrode in the first exemplary embodiment and in a conventionalexample;

FIG. 11 illustrates the relationship between an oxide film thickness andan electric resistivity in a pad according to the first exemplaryembodiment and in a pad according to the conventional example;

FIG. 12 illustrates a step of the method for manufacturing asemiconductor device according to the first exemplary embodiment; and

FIG. 13 illustrates a step of the method for manufacturing asemiconductor device according to the first exemplary embodiment.

In the drawing, numerals have the following meanings. 1: semiconductorsubstrate (silicon substrate), 2: STI, 3: active region, 4: gateinsulating film, 5: gate electrode, 6, 14, 31: insulating film, 7:sidewall insulating film, 8, 8 a, 8 b: diffusion layer, 9: firstinterlayer insulating film, 10, 10 a, 10 b: first contact plug, 11:second interlayer insulating film, 12: second contact plug, 13: firstwiring, 15: sidewall insulating film, 16: third interlayer insulatingfilm, 17: third contact plug, 18: contact pad, 18 a: diffusionpreventing film, 18 b: first conductive film, 18 c: sacrifice film(second conductive film), 18A: dummy pad, 19: cover film, 20: fourthinterlayer insulating film, 21: support film, 21A, 21B: openings, 22:lower electrode, 22A: dummy electrode, 23: capacitive insulating film,24: upper electrode, 25: capacitor, 26: fifth interlayer insulatingfilm, 27: fourth contact plug, 28: second wiring, 29: fifth contactplug, 30: third wiring, 32: sidewall insulating film, 33: sixth contactplug, 35: mask film, 35A, 35B: openings, 36: cylinder hall, 36A: dummyhole, 100: semiconductor device, 101: memory cell region, 102:peripheral circuit region.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention will be now described herein with reference toillustrative embodiments. Those skilled in the art will recognize thatmany alternative embodiments can be accomplished using the teachings ofthe present invention and that the invention is not limited to theembodiments illustrated for explanatory purposes.

A semiconductor device according to an exemplary embodiment will bedescribed below in detail with reference to the attached drawings,taking a DRAM (Dynamic Random Access Memory) as an example.

FIG. 1 is a conceptual drawing showing a planar structure of a DRAM thatis an example of semiconductor device 100 according to an exemplaryembodiment. The DRAM as the semiconductor device according to theexemplary embodiment is generally formed of memory cell regions 101 andperipheral circuit region 102. A plurality of memory cell regions 101are arranged on the DRAM. Peripheral circuit region 102 is arranged tosurround memory cell regions 101. Peripheral circuit region 102 includesa sense amplifier circuit, a word line driving circuit, and aninput/output circuit for external devices (these circuits are not shownin the drawings). In addition, the layout in FIG. 1 is illustrative, andthe number and positions of memory cell regions 101 are not limited tothose in the layout in FIG. 1.

FIG. 2 is a schematic cross-sectional view showing the structure of theDRAM that is an example of semiconductor device 100 according to theexemplary embodiment. FIG. 2A shows peripheral circuit region A1 and endA2 of a memory cell region. FIG. 2B shows central portion A3 of thememory cell region. The end and central portion of the memory cellregion are collectively referred to as the memory cell region.

In the DRAM according to the present exemplary embodiment, a planar MOS(Metal Oxide Semiconductor) transistor is provided on semiconductorsubstrate 1 (hereinafter referred to as “silicon substrate 1”) in thememory cell region and in the peripheral circuit region. The planar MOStransistor is positioned in active region 3 surrounded by STI (ShallowTrench Isolation) 2 serving as an isolation region provided in siliconsubstrate 1. The planar MOS transistor includes gate insulating film 4provided on a surface of silicon substrate 1, gate electrode 5 coveringover gate insulating film 4, and diffusion layer 8 provided aroundsilicon substrate 1 under gate insulating film 4 and serving as a sourceand a drain. Moreover, a top surface portion and a side surface portionof gate electrode 5 are covered with insulating film 6 and sidewallinsulating film 7, respectively. Each of diffusion layers 8 ispositioned not immediately below gate insulating film 4 but in regionsof silicon substrate 1 where gate insulating film 4 is not formedthereon.

For convenience of description, two MOS transistors are shown in activeregion 3 in FIG. 2B. However, in actuality, several thousands to severalhundred thousands of MOS transistors are arranged therein. Each ofdiffusion layers 8 is positioned in an upper part of silicon substrate1, covered with first interlayer insulating film 9, and is adapted tohave a conductivity type opposite to that of impurities in siliconsubstrate 1.

In the memory cell region, first contact plug 10 connected to each ofdiffusion layers 8 is provided so as to penetrate through firstinterlayer insulating film 9 and positioned between sidewall insulatingfilms 7 of adjacent planar MOS transistors. Here, first contact plug 10a connected to diffusion layer 8 a is connected to second contact plug12 provided so as to penetrate through second interlayer insulating film11. Furthermore, first contact plugs 10 b connected to diffusion layer 8b are connected to respective third contact plugs 17 provided so as topenetrate through second interlayer insulating film 11 and thirdinterlayer insulating film 16. Additionally, first wiring 13 serving asa bit line is positioned on second interlayer insulating film 11 so asto be covered with insulating film 14 and sidewall insulating film 15.First wiring 13 is connected to second contact plug 12.

Contact pads 18 are provided on third interlayer insulating film 16 soas to ensure an alignment margin between cylindrical capacitor 25 andeach third contact plug 17. Each contact pad 18 is connected tocorresponding third contact plug 17, positioned under contact pad 18.Here, contact pad (conductor film) 18 has a three-layer structure withdiffusion preventing film 18 a as a lowermost layer, first conductivefilm 18 b as an intermediate layer, and sacrifice film (secondconductive film) 18 c as an uppermost layer. As described below withreference to FIG. 10, an oxide film is formed on sacrifice film 18 c.However, the oxide film and the lower electrode are formed of the sameoxide film, and thus the oxide film is not shown in pad 18 in FIG. 2.This also applies to the drawings subsequent to FIG. 2.

Cylindrical capacitors 25 each including lower electrode 22, capacitiveinsulating film 23, and upper electrode 24 are provided on respectivecontact pad (conductor film) 18 so as to penetrate through cover film 19that protects fourth interlayer insulating film 20 and third interlayerinsulating film 16. Lower electrode 22 is connected to each contact pad18. Here, when the electric resistivity of contact pad 18 increases, theelectrical characteristics of capacitor 25 are degraded to causesemiconductor device 100 to malfunction.

Moreover, a side surface portion of cylindrical capacitor 25 isconnected to support film 21 arranged to prevent cylindrical capacitor25 from being collapsed so that adjacent cylindrical capacitors 25 cansupport each other. On cylindrical capacitor 25, at an end of the memorycell region, fourth contact plug 27 connected to upper electrode 24 isprovided in fifth interlayer insulating film 26 covering upper electrode24. Fourth contact plug 27 is connected to second wiring 28 positionedon fifth interlayer insulating film 26.

In the peripheral circuit region, fifth contact plug 29 connected todiffusion layer 8 is provided to penetrate through first interlayerinsulating film 9 and second interlayer insulating film 11. Furthermore,third wiring 30 is positioned on second interlayer insulating film 11 soas to be covered with insulating film 31 and sidewall insulating film32. Third wiring 30 is connected to fifth contact plug 29. A top surfaceof third wiring 30 is covered with cover film 19. Moreover, fourthinterlayer insulating film 20 and fifth interlayer insulating film 26are provided on cover film 19. Sixth contact plug 33 is arranged so asto penetrate through each of fourth interlayer insulating film 20 andfifth interlayer insulating film 26. Sixth contact plug 33 connectssecond wiring 28 and third wiring 30 together.

In connection with the DRAM configured as described above, a method formanufacturing semiconductor device 100 according to the presentinvention is mainly used for steps of manufacturing contact pad 18 andcapacitor 25. Thus, the manufacturing method will be described withreference to FIG. 3 to FIG. 13. In FIG. 3 to FIG. 9, FIG. 12, and FIG.13, subfigure A is a plan view of the peripheral circuit region and theend and central portion of the memory cell region. Subfigure B is across-sectional view taken along line A-A in subfigure A. Furthermore,in subfigure A, components on the surface in the correspondingmanufacturing step are shown by solid lines. The main componentsarranged below the surface are shown by dashed lines.

As shown in FIG. 3, active region 3 was formed on silicon substrate 1 byusing a silicon oxide film (SiO₂) or a silicon nitride film (SiN) toform STI 2 serving as an isolation region. Then, gate insulating film 4,gate electrode 5, and insulating film 6 were sequentially deposited onsilicon substrate 1; gate insulating film 4 that was a silicon oxidefilm, was formed by a thermal oxidation method, gate electrode 5 wasformed by depositing polysilicon by a thermal CVD (Chemical VaporDeposition) method or depositing tungsten (W) by a CVD method, andinsulating film 6 was formed by depositing a silicon nitride film by aplasma CVD method. Then, dry etching was carried out using insulatingfilm 6 as a mask to form gate electrode 5 of the planar MOS transistor.The side surface portion of gate electrode 5 was covered with sidewallinsulating film 7 that was a silicon nitride film by a thermal CVDmethod.

Then, diffusion layers 8 were formed in silicon substrate 1 around gateelectrode 5 by an ion injection method. Moreover, first interlayerinsulating film 9 was formed so as to bury the transistor using SOD(Spin On Dielectric) that were a coating insulating material. Firstinterlayer insulating film 9 was flattened by a CMP (Chemical MechanicalPolishing) method. Moreover, a photo resist (not shown in the drawings)was coated on first interlayer insulating film 9. A hole pattern with adesired shape was formed on a desired region of diffusion layer 8 byphotolithography. Then, dry etching was carried out using the holepattern (not shown in the drawings) as a mask to form a first hole (notshown in the drawings) in first interlayer insulating film 9.

Then, the first hole was buried using a conductive film such aspolysilicon deposited by the thermal CVD method or tungsten deposited bythe CVD method. Thereafter, an excess part of the conductive film onfirst interlayer insulating film 9 was removed by CMP to form firstcontact plug 10. In this case, first contact plug 10 is connected todiffusion layer 8.

Second interlayer insulating film 11 was formed on first interlayerinsulating film 9 by depositing a silicon oxide film using the plasmaCVD method. Then, in a manner similar to that described above, a secondhole (not shown in the drawings) was formed in second interlayerinsulating film 11 by photolithography and dry etching. Moreover, aconductive film such as tungsten was formed and CMP treatment wascarried out to form second contact plug 12 on a part of a memory cellregion in which the conductive film was buried and to form fifth contactplug 29 in the peripheral circuit region. Here, second contact plug 12is connected to first contact plug 10, and fifth contact plug 29 isconnected to diffusion layer 8.

Furthermore, tungsten (W) was deposited on second interlayer insulatingfilm 11 by the sputter method, and a silicon nitride film was depositedon second interlayer insulating film 11 by the plasma CVD method. Then,these films were separated from one another (patterning) byphotolithography and dry etching to form first wiring 13 in the memorycell region and to form third wiring 30 in the peripheral circuitregion. In this case, insulating film 14 is stacked on a top surface offirst wiring 13, which is connected to second contact plug 12.Insulating film 31 is stacked on the top surface of third wiring 30,which is connected to fifth contact plug 29. A side surface portion offirst wiring 13 was covered with sidewall insulating film 15 such as asilicon nitride film deposited by the thermal CVD method, and at thesame time, a side surface portion of third wiring 30 was covered withsimilar sidewall insulating film 32. Then, the respective pieces ofwiring were covered with third interlayer insulating film 16 that wasSOD. Thereafter, the third interlayer insulating film 16 was flattenedby CMP.

Then, a photo resist (not shown in the drawings) was coated on thirdinterlayer insulating film 16. A hole pattern (not shown in thedrawings) was formed on the photo resist on desired first contact plug10 by photolithography. Moreover, dry etching was carried out to form athird hole (not shown in the drawings) in second interlayer insulatingfilm 11 and third interlayer insulating film 16. Then, the third holewas buried using a conductive film such as polysilicon deposited by thethermal CVD method or tungsten deposited by the CVD method. Thereafter,an excess part of the conductive film on third interlayer insulatingfilm 16 was removed by CMP treatment to form third contact plug 17.Here, third contact plug 17 is connected to first contact plug 10.

As shown in FIG. 4, the sputter method was used to form diffusionpreventing film 18 a, first conductive film 18 b, and sacrifice film(second conductive film) 18 c so that the films 18 a, 18 b, and 18 ccover third contact plug 17; diffusion preventing film 18 a was tungstennitride (WN) with a thickness of 10 nm, first conductive film 18 b wastungsten (W) (first metal) with a thickness of 30 nm, and sacrifice film(second conductive film) 18 c was molybdenum (Mo) (second metal) with athickness of 10 nm. At this time, deposition conditions for molybdenumwere as follows:

A magnetron sputter method using a molybdenum target was used. Argon(Ar) was used as process gas. For argon, flow rate and power supply ACoutput were set to 30 sccm (standard cubic centimeter per minute), 1,000W, respectively, and temperature and pressure were set to 25° C. and 1.0Pa, respectively.

Moreover, diffusion preventing film 18 a, first conductive film 18 b,and sacrifice film 18 c were patterned to form contact pad 18 with adiameter of 100 nm by photolithography and dry etching. In this dryetching, first, sacrifice film 18 c was etched, and then remaining firstconductive film 18 b and diffusion preventing film 18 a were etched.Sacrifice film 18 c was dry etched using tetrachlorosilane (SiCl₄),oxygen (O₂), and trifluoromethane (CHF₃) as process gas. Furthermore,dry etching conditions for first conductive film 18 b and diffusionpreventing film 18 a were as follows:

Sulfur hexafluoride (SF₆), oxygen (O₂), and argon (Ar) were used asprocess gas, and the respective flow rates were set to 70 sccm (SF₆), 30sccm (O₂), and 120 sccm (Ar). Source power was set to 600 W to 1,200 W,bias power was set to 50 W to 200 W, and pressure was set to 4 mTorr to20 mTorr.

Here, diffusion preventing film 18 a forming contact pad 18 is connectedto third contact plug 17.

Moreover, here, simultaneously with the formation of contact pad 18,dummy pad 18A was formed so as to surround contact pad 18. Like contactpad 18, dummy pad 18A is formed of diffusion preventing film 18 a, firstconductive film 18 b, and sacrifice film (second conductive film) 18 c.In this case, molybdenum is used as a second metal forming sacrificefilm 18 c. However, metal such as cobalt (Co), ruthenium (Ru), chromium(Cr), or manganese (Mn) may be used as a second metal instead ofmolybdenum.

As shown in FIG. 5, as a protective film for third interlayer insulatingfilm 16 used during wet etching of fourth interlayer insulating film 20described below, cover film 19 was deposited so as to cover contact pad18, dummy pad 18A, and third interlayer insulating film 16. Here, coverfilm 19 may be a silicon nitride film of thickness 50 nm deposited bythe thermal CVD method. Then, fourth interlayer insulating film 20 thatwas a silicon oxide film of thickness 1,600 nm was deposited on coverfilm 19 by the plasma CVD method.

As shown in FIG. 6, support film 21 that was a silicon nitride film ofthickness 50 nm was deposited by the plasma CVD method so as to coverfourth interlayer insulating film 20. Then, groove-like openings 21Awith width X1 of 70 nm were formed in support film 21 byphotolithography and dry etching to expose parts of fourth interlayerinsulating film 20. At this time, openings 21A extended in a Y directionand were arranged parallel to one another in an X direction so as tooverlap fourth interlayer insulating film 20 on contact pad 18 as seenin a plan view at intervals X2 of 70 nm. In this case, opening 21A isshaped like a groove but may be shaped like a hole of diameter 70 nm. Inaddition, simultaneously with the formation of openings 21A, opening 21Bwith width X1 of 70 nm was formed. Opening 21B was arranged so as tooverlap fourth interlayer insulating film 20 on dummy pad 18A as seen ina plan view and to surround openings 21A.

As shown in FIG. 7, mask film 35 that was a silicon oxide film ofthickness 100 nm was deposited by the plasma CVD method so as to buryopenings 21A and 21B and to cover support film 21. Then, hole-likeopenings 35A each with diameter X3 of 70 nm was formed in mask film 35by photolithography and dry etching. In this case, since openings 35Aare positioned so as to overlap openings 21A as seen in a plan view,parts of fourth interlayer insulating film 20 exposed by openings 21Aare exposed by openings 35A. In addition, simultaneously with theformation of openings 35A, opening 35B with width X3 of 70 nm wasformed. Opening 35B is arranged so as to overlap at least a part ofopening 21B as seen in a plan view and surrounds openings 35A.

As shown in FIG. 8, parts of fourth interlayer insulating film 20 whichwere exposed at the bottom of openings 35A were removed by dry etchingusing openings 21A and 35A as a mask. Thus, cylinder holes 36 wereformed which passed through from mask film 35 through support film 21 tofourth interlayer insulating film 20. As a result of this dry etching,each cylinder hole 36 formed in fourth interlayer insulating film 20 hasdiameter X4 of 70 nm, which is the same as that of each opening 35A,thus exposing a part of cover film 19. Moreover, the dry etching is setto offer high selectivity so as to etch only the parts of fourthinterlayer insulating film 20 exposed by openings 35A. Thus, mask film35 and cover film 19 remain in the same state as that before the dryetching. Simultaneously with the formation of cylinder hole 36, dummyhole 36A with width X4 of 70 nm was formed by dry etching using openings21B and 35B as a mask. Like cylinder holes 36, dummy hole 36A exposes apart of cover film 19.

Then, parts of cover film 19 each remaining on a bottom surface ofcorresponding cylinder hole 36 were removed by dry etching, to expose atleast part of corresponding contact pad 18. In this case, dry etchingconditions were as follows:

Trifluoromethane (CHF₃) and oxygen (O₂) were used as material gas, andthe respective flow rates were set to 80 sccm (CHF₃) and 20 sccm (O₂).High frequency power, stage temperature, and pressure were set to 3,000W, 20° C., and 30 mTorr, respectively.

This dry etching was set to offer high selectivity so as to etch onlyparts of cover film 19 exposed by cylinder holes 36. Thus, mask film 35and contact pads 18 remained without being etched. As a result of thedry etching, a part of sacrifice film 18 c included in contact pad 18was exposed at the bottom surface of cylinder hole 36. Here, the surfaceof sacrifice film 18 c formed of molybdenum was exposed to oxygen (O₂)forming the material gas for the dry etching. However, an oxide such asmolybdenum dioxide was not formed. This is because molybdenum has theproperty of avoiding reacting with oxygen (O₂) at room temperature. Thisalso applies to tungsten (W) forming first conductive film 18 b.Simultaneously with the removal of parts of cover film 19 which remainon the bottom surfaces of respective cylinder holes 36, a part of coverfilm 19 which remained on a bottom surface of dummy hole 36A was removedto expose at least a part of dummy pad 18A.

As shown in FIG. 9, lower electrode 22 that was molybdenum dioxide(MoO₂) of thickness 10 nm was formed by the ALD (Atomic LayerDeposition) method so as to cover an inner wall of cylinder hole 36.Simultaneously with the formation of lower electrode 22, dummy electrode22A that was molybdenum dioxide (MoO₂) of thickness 10 nm was formed bythe ALD method so as to cover an inner wall of dummy hole 36A. Accordingto the ALD method, a cycle was repeatedly carried out a plurality oftimes to deposit the relevant film on the silicon substrate maintainedat a predetermined temperature. The cycle includes:

(1) Supplying material gas and adsorbing the material on the exposedsurface (body in which a film is to be deposited; sacrifice film 18 c)of contact pad 18,(2) discharging a non-adsorbed portion of the material gas by vacuumpurging,(3) supplying oxidizing gas to oxidize the adsorbed material, and(4) discharging an excess portion of the oxidizing gas by vacuumpurging.

Here, step (1) was carried out for 45 seconds under the followingprocess conditions for one cycle:

TEMAM (Tetrakis Ethyl Methyl Amide Molybdenum: Mo[N(CH₃)CH₂CH₃]₄) wasused as material gas, and for the material gas, flow rate, temperature,and pressure were set to 100 sccm, 130° C., and 0.8 Torr, respectively.

step (3) was carried out for 15 seconds under the following conditions:

Ozone (O₃) was used as oxidizing gas, and for the oxidizing gas, flowrate, temperature, and pressure were set to 800 sccm, 130° C., and 0.8Torr, respectively.

These process conditions allow lower electrode 22 of thickness 0.3 nm tobe formed per cycle, and thus 33 cycles of treatment were carried out toachieve a thickness of 10 nm. A part of lower electrode 22 also covereda top surface of mask film 35, and thus the part of lower electrode 22on mask film 35 was removed by CMP. In addition, in view of thedeposition speed of molybdenum dioxide (MoO₂), cycle formed of steps (1)to (4) are preferably carried out at 150° C. to 300° C.

The ALD method uses ozone (O₃), which has higher oxidizability thanoxygen (O₂), to oxidize the material at high temperature (for example,150° C. to 300° C.). Thus, the surface of contact pad 18, which is notoxidized by oxygen, is oxidized. FIG. 10 includes differentcross-sectional views showing how first conductive film 18 b andsacrifice film 18 c forming contact pad 18 are oxidized with ozone. Inaddition, the oxidation of first conductive film 18 b does not occur inthe present exemplary embodiment but is shown to clarify differencesfrom the conventional technique. According to the present exemplaryembodiment, sacrifice film 18 c is exposed at the bottom portion ofcylinder hole 36 when lower electrode 22 is formed, whereas according tothe conventional technique, first conductive film 18 b is exposed at thebottom portion of cylinder hole 36 when lower electrode 22 is formed.Thus, the manner in which the surface of contact pad 18 is oxidizedvaries between the present exemplary embodiment and the conventionaltechnique. More specifically, as shown in FIG. 10, according to thepresent exemplary embodiment, molybdenum dioxide (MoO₂) (an oxide filmof the second metal) is formed on the surface of sacrifice film 18 c asa result of oxidation of molybdenum (Mo) (second metal) formingsacrifice film 18 c. On the other hand, according to the conventionaltechnique, tungsten dioxide (WO₂) (an oxide film of the first metal) isformed on the surface of first conductive film 18 b as a result ofoxidation of tungsten (W) (first metal) forming first conductive film 18b. In the actual structure according to the present exemplaryembodiment, the molybdenum dioxide (MoO₂) formed on the surface ofsacrifice film 18 c is the same as the molybdenum dioxide (MoO₂) formedinto the lower electrode. Hence, the boundary between these layers ofmolybdenum dioxide (MoO₂) may not be clearly determined. However, a topsurface of the contact pad normally has a cross-sectional shapedifferent from that of a bottom surface of the lower electrode, and thusa discontinuous portion of the cross-sectional shape may be identifiedas the boundary between the contact pad and the lower electrode.

FIG. 11 shows the electric resistance of the structure containingmolybdenum dioxide (the oxide film of the second metal) and of thestructure containing tungsten dioxide (the oxide film of the firstmetal). Here, FIG. 10A shows first conductive film 18 b of diameter 70nm and thickness 40 nm as a conventional structure. Furthermore, in thestructure according to the exemplary embodiment shown in FIG. 10B, firstconductive film 18 b is set to 30 nm in thickness so as to set the totalfilm thickness of first conductive film 18 b of diameter 70 nm andsacrifice film 18 c to 40 nm. Thus, the electric resistance in FIG. 11is based on the film thickness and bottom area shown in FIG. 10. Inaddition, the thicknesses of first conductive film 18 b and sacrificefilm 18 c, from which the oxide is obtained, decrease with increasingoxide film thickness. The electric resistance in FIG. 11 is shown withsuch a structural variation taken into account. As shown in FIG. 11, atany oxide film thickness, the electric resistance of the contact pad inthe exemplary embodiment structure containing molybdenum dioxide islower than that of the contact pad in the conventional structurecontaining tungsten dioxide. The reason why the electric resistanceshows such a characteristic is that molybdenum dioxide (the oxide filmof the second metal) has an electric resistivity of 400 μΩ·cm, whereastungsten dioxide (the oxide film of the first metal) has an electricresistivity of 5,000 μΩ·cm; the electric resistivity of molybdenumdioxide accounts for only 8% of the electric resistivity of tungstendioxide. An oxide can also be obtained even if metal such as cobalt(Co), ruthenium (Ru), chromium (Cr), or manganese (Mn) is used forsacrifice film 18 c instead of molybdenum. Oxides of these metals have alower electric resistivity than tungsten dioxide (the oxide film of thefirst metal) and thus serve to exert effects similar to those ofmolybdenum.

The oxide film of the second metal preferably has an electricresistivity of 1,000 μΩ·cm or less. Such an electric resistivity enablesa reduction in the resistance of contact pad 18. That is, the secondmetal serving as a material for sacrifice film 18 c is selected suchthat the oxide film of the second metal has a lower electric resistivitythan the oxide film of the first metal obtained by oxidizing the firstmetal serving as a material for first conductive film 18 b. The effectsof the present invention can be exerted if for example, sacrifice film18 c contains, as the second metal, at least one type of metal selectedfrom a group consisting of molybdenum (Mo), cobalt (Co), ruthenium (Ru),chromium (Cr), and manganese (Mn). If molybdenum (Mo), cobalt (Co),ruthenium (Ru), chromium (Cr), or manganese (Mn) is used as the secondmetal, molybdenum dioxide (MoO₂), cobalt dioxide (CoO₂), rutheniumdioxide (RuO₂), chromium dioxide (CrO₂), or manganese dioxide (MnO₂),respectively, is formed on the surface of sacrifice film 18 c after thelower electrode is formed.

In the above-described example, second conductive film 18 c is 10 nm infilm thickness before lower electrode 22 is formed. However, the filmthickness of second conductive film 18 c is not limited to this rangebut may be 2 nm to 20 nm. When the film thickness of second conductivefilm 18 c falls within these ranges, the oxide film of the second metalmay have a predetermined range of film thickness after the lowerelectrode is formed, thereby enabling an effective reduction in theresistance of the contact pad. The oxide film of the second metalpreferably has a film thickness of 1 nm to 5 nm after lower electrode 22is formed.

Furthermore, after lower electrode 22 is formed, the second conductivefilm may remain or second conductive film 18 c may wholly be convertedinto an oxide film of the second metal. If second conductive film 18 cremains after lower electrode 22 is formed, when second conductive film18 c has a higher electric resistivity than first conductive film 18 b,the electric resistivity of the contact pad as a whole increases by thedifference in electric resistivity. However, since both first and secondconductive films 18 b and 18 c are conductive, there is not a greatdifference between these films in electric resistivity. In contrast, asdescribed above, the oxide film of the second metal has a significantlylower electric resistivity than the oxide film of the first metal. Thus,even if an increase in the electric resistivity of second conductivefilm 18 c with respect to first conductive film 18 b is taken intoaccount, since the electric resistivity of the oxide film of the secondmetal decreases with respect to the oxide film of the first metal, theelectric resistivity of the pad as a whole decreases. Thus, the effectsof the present invention can be exerted even if second conductive film18 c has a higher electric resistivity than first conductive film 18 b.However, to allow a further reduction in the electric resistivity of thepad as a whole, the material of second conductive film 18 c ispreferably selected to achieve a lower electric resistivity than firstconductive film 18 b.

If second conductive film 18 c remains after lower electrode 22 isformed, the film thickness ratio between second conductive film 18 c andthe oxide film of the second metal is preferably such that (the filmthickness of the second conductive film):(the film thickness of theoxide film of the second metal)=20:1 to 2:1.

As shown in FIG. 12, mask film 35, formed of a silicon oxide film, and apart of fourth interlayer insulating film 20 which was located in thememory cell region were removed by wet etching using hydrofluoric acid(HF) to expose the side surface portion of lower electrode 22. The wetetching is isotropic and thus allows the removal not only of parts offourth interlayer insulating film 20 which are exposed from openings 21Aappearing after the removal of mask film 35 but also of a part of fourthinterlayer insulating film 20 which is located under support film 21. Atthis time, a part of fourth interlayer insulating film 20 which islocated in the peripheral circuit region remains without being etchedbecause this part is entirely covered with support film 21 and dummyelectrode 22A, which are not removed by hydrofluoric acid. Parts ofcover film 19 which are newly exposed by the removal of the part offourth interlayer insulating film 20 which is located in the memory cellregion, are also not removed by hydrofluoric acid and thus remain in thesame state as that before the wet etching.

As shown in FIG. 13, capacitive insulating film 23 was formed by the CVDmethod or the ALD method so as to cover the surface of lower electrode22 with the side surface thereof exposed. Thereafter, upper electrode 24that was molybdenum dioxide was deposited by the ALD method so as tofurther cover the surface of capacitive insulating film 23. Lowerelectrode 22 and upper electrode 24 thus arranged opposite to each othervia capacitive insulating film 23 function as a capacitor. Capacitiveinsulating film 23 may be a high-dielectric-constant film such astitanium oxide (TiO₂), zirconium oxide (ZrO₂), aluminum oxide (Al₂O₃),or hafnium oxide (HfO₂), or a film stack thereof. Furthermore, upperelectrode 24 may have a stack structure obtained by forming molybdenumdioxide of thickness about 10 nm, stacking a polysilicon film withimpurities doped therein on the molybdenum dioxide to fill a cavityportion between adjacent lower electrodes 22, and further depositingtungsten (W) on the polysilicon film to a thickness of about 100 nm.Additionally, the upper electrode may be at least one type of oxide filmselected from a group consisting of molybdenum dioxide (MoO₂), manganesedioxide (MnO₂), chromium dioxide (CrO₂), cobalt dioxide (CoO₂), andruthenium dioxide (RuO₂), or a metal film such as ruthenium (Ru) orplatinum (Pt).

Then, unwanted films (upper electrode 24, capacitive insulating film 23,and support film 21) on the peripheral circuit region were removed bydry etching using a photoresist film (not shown in the drawings) as amask to form capacitor 25. Removal of support film 21 from theperipheral circuit region allows easy formation of deep contact plugspenetrating through the part of fourth interlayer insulating film 20which is located in the peripheral circuit region.

Then, a top surface of upper electrode 24 is covered with fifthinterlayer insulating film 26 formed of a silicon oxide film or thelike. Fifth interlayer insulating film 26 is flattened by CMP. Then,fourth contact plug 27 and second wiring 28 are formed which served toprovide a predetermined potential to upper electrode 24. Semiconductordevice 100 as a DRAM shown in FIG. 2 is completed by subsequentformation of a surface protection film and the like.

As described above, in semiconductor device 100 according to the presentexemplary embodiment, contact pad (conductor film) 18 is formed byforming sacrifice film 18 c on first conductive film 18 b. With the thusformed contact pad, even if the surface of contact pad 18 is oxidized byozone when lower electrode 22 is formed, only sacrifice film 18 c theoxide of which has a low electric resistivity is oxidized. This preventsoxidation of first conductive film 18 b the oxide of which has a highelectric resistivity. Such an oxidation prevention effect of firstconductive film 18 b suppresses an increase in the electric resistivityof contact pad 18 to reduce the malfunction rate of semiconductor device100. This enables an increase in yield.

Furthermore, as described in FIG. 10 and FIG. 11, the material ofsacrifice film 18 c is selected such that the oxide film formed on thesurface of sacrifice film 18 c has a lower electric resistivity than theoxide film formed on the surface of first conductive film 18 b.Moreover, second conductive film 18 c preferably has a lower electricresistivity than first conductive film 18 b. Thus, when secondconductive film 18 c and the oxide film of the second metal each have alower electric resistivity than the corresponding one of firstconductive film 18 b and the oxide film of the first metal, the electricresistivity of the whole pad including first conductive film 18 b,second conductive film 18 c, and the oxide film of the second metalaccording to the present embodiment can be set lower than that of a padwith first conductive film 18 b and the oxide film of the first metal.

The exemplary embodiment has been described. However, the presentinvention is not limited to the exemplary embodiment. Various changesmay be made to the exemplary embodiment without departing from the scopeof the present invention, and the resulting embodiments are of courseincluded within the scope of the present invention.

It is apparent that the present invention is not limited to the aboveembodiments, but may be modified and changed without departing from thescope and spirit of the invention.

Moreover, the scope of the present invention includes the followingmanufacturing methods.

1. A method for manufacturing a semiconductor device, comprising:

forming a conductor including a first conductive film containing a firstmetal, a second conductive film containing a second metal on the firstconductive film, and an oxide film of the second metal on the secondconductive film; and

forming a lower electrode of a capacitor on the conductor,

wherein the oxide film of the second metal has a lower electricresistivity than an oxide film of the first metal.

2. The method for manufacturing a semiconductor device according to theabove 1,

wherein the lower electrode of the capacitor is formed by an ALD method.

3. The method for manufacturing a semiconductor device according to theabove 2,

wherein in the ALD method, a cycle formed of the following steps (1)-(4)is performed one or more times:

(1) supplying material gas to adsorb a material on an exposed surface ofthe conductor;

(2) purging the material gas;

(3) supplying oxidizing gas to oxidize the adsorbed material; and

(4) purging the oxidizing gas.

4. The method for manufacturing a semiconductor device according to theabove 3,

wherein the oxidizing gas is ozone (O₃) gas.

5. The method for manufacturing a semiconductor device according to theabove 1,

wherein the second metal is at least one type of metal selected from thegroup consisting of molybdenum (Mo), cobalt (Co), ruthenium (Ru),chromium (Cr), and manganese (Mn).

6. The method for manufacturing a semiconductor device according to theabove 1,

wherein the first metal is tungsten.

7. The method for manufacturing a semiconductor device according to theabove 1,

wherein in forming the conductor, the oxide film of the second metalhaving the electric resistivity of 1,000 μΩ·cm or less is formed.

8. The method for manufacturing a semiconductor device according to theabove 1,

wherein in forming the lower electrode of the capacitor, the lowerelectrode is formed which contains at least one type of oxide filmselected from the group consisting of molybdenum dioxide (MoO₂),manganese dioxide (MnO₂), chromium dioxide (CrO₂), cobalt dioxide(CoO₂), and ruthenium dioxide (RuO₂).

9. The method for manufacturing a semiconductor device according to theabove 1, further comprising, after forming the lower electrode of thecapacitor, forming a capacitive insulating film of the capacitor on thelower electrode.

10. The method for manufacturing a semiconductor device according to theabove 9,

wherein in forming the capacitive insulating film, the capacitiveinsulating film containing titanium dioxide is formed.

11. The method for manufacturing a semiconductor device according to theabove 9, further comprising, after forming the capacitive insulatingfilm, forming an upper electrode containing at least one type of oxidefilm selected from the group consisting of molybdenum dioxide (MoO₂),manganese dioxide (MnO₂), chromium dioxide (CrO₂), cobalt dioxide(CoO₂), and ruthenium dioxide (RuO₂), on the capacitive insulating film.

What is claimed is:
 1. A semiconductor device comprising: a conductorwhich includes a first conductive film containing a first metal, asecond conductive film containing a second metal on the first conductivefilm, and an oxide film of the second metal on the second conductivefilm; and a capacitor comprising a lower electrode provided on theconductor, wherein the oxide film of the second metal has a lowerelectric resistivity than an oxide film of the first metal.
 2. Thesemiconductor device according to claim 1, wherein the second metal isat least one type of metal selected from the group consisting ofmolybdenum (Mo), cobalt (Co), ruthenium (Ru), chromium (Cr), andmanganese (Mn).
 3. The semiconductor device according to claim 1,wherein the first metal is tungsten.
 4. The semiconductor deviceaccording to claim 1, wherein the oxide film of the second metal has theelectric resistivity of 1,000 μΩ·cm or less.
 5. The semiconductor deviceaccording to claim 1, wherein the lower electrode contains at least onetype of oxide film selected from the group consisting of molybdenumdioxide (MoO₂), manganese dioxide (MnO₂), chromium dioxide (CrO₂),cobalt dioxide (CoO₂), and ruthenium dioxide (RuO₂).
 6. Thesemiconductor device according to claim 1, wherein the capacitorcomprises a capacitive insulating film formed on the lower electrode. 7.The semiconductor device according to claim 6, wherein the capacitiveinsulating film contains titanium dioxide.
 8. The semiconductor deviceaccording to claim 6, wherein the capacitor includes an upper electrodeformed on the capacitive insulating film, the upper electrode containingat least one type of oxide film selected from the group consisting ofmolybdenum dioxide (MoO₂), manganese dioxide (MnO₂), chromium dioxide(CrO₂), cobalt dioxide (CoO₂), and ruthenium dioxide (RuO₂).
 9. Thesemiconductor device according to claim 8, further comprising: a contactplug connected to the conductor; and a transistor including a diffusionlayer connected to the contact plug.
 10. The semiconductor deviceaccording to claim 1, wherein the second conductive film has a filmthickness of 2 nm or more and 20 nm or less.
 11. The semiconductordevice according to claim 1, wherein the oxide film of the second metalhas a film thickness of 1 nm or more and 5 nm or less.
 12. Thesemiconductor device according to claim 1, further comprising adiffusion preventing film under the first conductive film.
 13. Thesemiconductor device according to claim 12, wherein the diffusionpreventing film contains tungsten nitride.
 14. A semiconductor devicecomprising: a first conductive film containing a first metal; a secondconductive film containing a second metal on the first conductive film;an oxide film of the second metal on the second conductive film; and athird conductive film on the oxide film of the second metal, wherein theoxide film of the second metal has a lower electric resistivity than anoxide film of the first metal.
 15. The semiconductor device according toclaim 14, wherein the first metal is tungsten.
 16. The semiconductordevice according to claim 14, wherein the second metal is at least onetype of metal selected from the group consisting of molybdenum (Mo),cobalt (Co), ruthenium (Ru), chromium (Cr), and manganese (Mn).
 17. Thesemiconductor device according to claim 14, wherein the oxide film ofthe second metal has the electric resistivity of 1,000 μΩ·cm or less.18. The semiconductor device according to claim 14, wherein the secondconductive film has a film thickness of 2 nm or more and 20 nm or less.19. The semiconductor device according to claim 14, wherein the oxidefilm of the second metal has a film thickness of 1 nm or more and 5 nmor less.
 20. The semiconductor device according to claim 14, furthercomprising a diffusion preventing film under the first conductive film.